Jonathan,
I have two iPhone Xs, an A1905 model and an A1865 model. Both are equally unreliable at cell service. I expect that both are equally unreliable at data (using the web) although I've had most of that trouble using the A1905 because...
I have an iPhone 8 that is used pretty much exclusively as a hotspot for other devices. It has been fairly reliable in this role, though it is NEVER used while I'm moving around, only when I'm settled somewhere. Because both iPhone Xs are so very unreliable I tend to do much more data / web stuff using an iPad through the iPhone 8 hotspot. I can NOT tell you that the iPhone 8 is a good reliable data phone, just that it's working OK in the limited role I have for it, and I hardly ever use it as a cell phone.
My iPhone 6s Plus was still fully-operational when these phones came out. I had it posted online to sell it after the first iPhone X (A1905) arrived, but within days took it down and have kept it. I now frequently have it with me along with an iPhone X because it continues to be a much more-reliable cell phone. I can drop or fail to make a call with the X, pick up the 6s Plus and immediately make the call successfully, sometimes in exactly the same location, sometimes just a short distance down the road.
My wife's iPhone 6 is still fully-operational. I've been in a few situations in which one or the other of my iPhone Xs will not connect to data or make a call, and her phone works perfectly. If you think she'd restrain herself from taunting me about spending so much money on two iPhone Xs that flat out don't work properly on cell networks (I've used mine on two different networks, in places all over North America) you'd be wrong.
All of our phones are carefully kept up to date with latest software. Don't let anyone tell you that these issues are related to iOS, or to your SIM card, or to your phone needing a reset, or to failings by the cell phone company. They are not. These "solutions" have been tried by many here, and they make no difference at all. There is an issue with the iPhone X hardware, and many of us are hoping that Apple steps up to it soon.